A day after the U.S. government suspended its delivery of F-35 to Turkey, Acting Defense Secretary Patrick Shanahan sounded confident that Turkey will get the planes after all.

“I expect them to be delivered,” Shanahan said on Tuesday at a media availability.

The Pentagon announced on Monday that F-35 deliveries to Turkey were being delayed because Turkey insisted on purchasing the Russian-made S-400 air defense system in July instead of Patriot missiles from the United States.

“The United States has been clear that Turkey's acquisition of the S-400 is unacceptable,” Pentagon spokesman Charles Summers said in a statement. “We very much regret the current situation facing our F-35 partnership with Turkey, and the DoD is taking prudent steps to protect the shared investments made in our critical technology. Our important dialogue on this matter will continue, however, until they forgo delivery of the S-400, the United States has suspended deliveries and activities associated with the stand-up of Turkey's F-35 operational capability. Should Turkey procure the S-400, their continued participation in the F-35 program is at risk.”

But on Tuesday, Shanahan expressed optimism that the Turkey would receive “the right defense equipment in terms of Patriots and F-35s” from the United States.

Shanahan also said he has had several discussions with Turkish Defense Minister Hulusi Akar indicating the current disagreement over the S-400 will be resolved.

“I am very confident in the Patriot proposal that we've delivered to Turkey, its availability, it's pricing, and very importantly, the industrial participation that comes along with the Patriot system,” he said.

Marine Gen. Joseph Dunford said the U.S. government “hasn't given up yet” on delivering the F-35s to Turkey, but he acknowledged that the issue is complicated.”

The S-400 and the F-35, we've made it very clear that those are incompatible systems,” Duford told reporters on Tuesday. “But we're still working our way through that and hope we can come up with an arrangement with Turkey.”

UPDATE: This story was updated on April 2 with comments from Marine Gen. Joseph Dunford.

SEE ALSO: On its first combat deployment, the Marine Corps' F-35 bombed both the Taliban and ISIS

WATCH NEXT: Pentagon Orders Entire F-35 Fleet Grounded